Biomass is considered an important source of energy. Particularly interesting candidates for exploiting the energy contained in biomass, e.g. for the production of heat or electrical energy, are biological materials that are otherwise considered as a waste product of agricultural crops, such as straw, corn stalks, or the like. At harvest, these biomaterials are dried, compressed and bound into bales suitable for transportation and storage.
A biomass energy plant may be a plant or installation for immediate energy production from biomaterials, such as heat or electrical energy, or may be a plant for the production of fuels for energy generation at a later stage. Examples of such biomass energy plants are a straw-fired boiler, a bio-ethanol production plant or a biomass pellet production plant. At industrial scale, such biomass energy plants require a large amount of dried biomaterial to be supplied at a fast rate. For example in a straw-fired energy plant, production rates may easily reach thirty tons per hour.
Biomaterial is usually delivered to and stored at the site of such biomass energy plant in the form of bales. For production, the bales are conveyed to the production unit of the plant via one or more feeding lines. In the feeding line, the biomaterials are processed into a form suitable to be supplied to the production unit of the plant.
This processing is performed using a bale opener for breaking up the bales and effectively loosening the biomaterial gently, but at a high rate suitable for industrial scale production, while avoiding lumps of compressed biomaterial that might choke the supply mechanism of the production unit, for example the stoker of a straw fired boiler.
Other problems that are particularly pronounced in industrial scale set-ups operating at high production rates and that are to be avoided is generation of sparks and/or the entanglement of bale packaging materials, in particular bale strings, in the mechanism of the feeding line.
Different types of equipment for processing bales of biomaterial for use in e.g. a straw fired burner are known in the art.
DE 32 09 885 discloses a straw bale comminution device for supplying a straw fired central heating boiler. The comminution device involves a single rotating disk cutting the straw by means of knives radially arranged thereon, the knives cooperation with edges of corresponding holes in a stator disk to provide a scissor action. Such a construction involving a comminution type processing mechanism requires frequent attention in order to maintain the knives sharp, and remove frequently encountered contaminants, such as stones, branches or even metal parts jammed in the comminution mechanism, here typically between the rotating disk and the stator disk, and in particular bale packaging materials, such as bale strings, entangled therein. Furthermore, when operating the device according to DE 32 09 885, a core of unprocessed material tends to build up in the central part around the rotation axis, thus leading to congestion in the feeding hopper. To avoid such a core from building up, additional cutting means may need to be provided at the hub part in the centre. Such cutting means rotating in the centre are particularly prone to catching bale strings subsequently getting entangled in the rotating parts.
A bale opener of the type mentioned in the introduction above is known from DK 173 159. DK 173 159 discloses a breaking-up device with at least two breaking-up means that are shaped as a body of revolution carrying a helicoid on the surface. The at least two breaking-up means are arranged next to each other and are at one end supported by bearings. The breaking-up means are operable to be rotated in such direction that the transport direction of the helicoid is directed away from the bearings. The configuration disclosed in DK 173 159 has the drawback that under operational conditions a considerable tilting load may occur in a transverse direction of the bearings of the breaking-up means. When mounted in connection with a feeding channel, the breaking-up device of DK 173 159 is hinged on a spring-loaded support such that the breaking-up device may swing away from the end of the feeding channel and give way to the pressure exerted on the breaking-up means by the straw bales conveyed thereto. The hinged support allows lumps of compacted straw to bypass the breaking-up device.